1. (Field of the Invention)
The present invention generally relates to an electric lighting device and, more particularly, to a recessed overhead lighting device of a type adapted to be encased in a ceiling in an architecture such as a reinforced concrete building or housing.
2. (Description of the Prior Art)
The recessed overhead lighting device now available in the market is generally supported by a ceiling in a suspended fashion in the following manner. During preparation of ceiling slabs by pouring a concrete material into molds, insert screws are embedded in predetermined locations in each ceiling slab so that upon completion of a building, the insert screws can extend downwardly from the concrete slab which partitions the interior of the building into upper and lower rooms. Each of the insert screws is adapted to threadingly receive an upper end of an externally threaded headless bolt.
On the other hand, a generally grid-patterned panel support frame-work including a plurality of elongated ceiling joist supports extending parallel to each other and spaced a predetermined pitch from each other, and a plurality of elongated ceiling joists extending parallel to each other and also extending transverse to the ceiling joist supports and spaced a predetermined pitch from each other is disposed immediately beneath the ceiling slab. Ceiling panels are subsequently secured to the ceiling joists to complete the ceiling.
The prior art lighting device is mounted in a mounting opening defined in one of the ceiling panels by inserting it from below into the mounting opening. At the time the prior art lighting device is inserted from below into the mounting opening, respective lower ends of the headless bolts embedded at their upper ends in the ceiling slab are, after having been bent to align with associated bearing holes defined in the lighting device, inserted into the associated bearing holes. Internally threaded nuts are then fastened from below to the lower ends of the respective bolts so that the prior art lighting device can be suspended from the ceiling slab in a fashion inserted in the mounting opening.
The mounting of the prior art lighting device described above involves numerous problems. For example, in the event that even the single insert screw has been inadvertently omitted by, for example, the reason that during the preparation of the ceiling slabs the attendant worker has forgotten to implant it in the mold, the concrete ceiling slab must be drilled so that an anchor bolt can be inserted into the concrete ceiling slab prior to the mounting of the lighting device. This is indeed a complicated and time-consuming job which ought not to have been performed.
Another problem occurs if the insert screws are not accurately positioned in the concrete ceiling slab. Inaccurate positioning of the insert screws in the concrete ceiling slab makes it difficult to install the lighting device relative to the ceiling and, even if it can be successfully installed, the skilled worker must exercise such a complicated and time-consuming job so that the lighting device can be supported stably. In addition, installation of the prior art lighting device requires a preparatory job of marking lines on the concrete slab for positioning purpose, resulting in an increase of the cost for installation of the prior art lighting device.
Considering that the prior art recessed overhead lighting device is supported solely by means of the headless bolts in a fashion suspended from the concrete slab, it has been found that the lighting device once installed tends to be considerably displaced sidewise relative to the ceiling panel in the event of occurrence of an earthquake, to such an extent as to collide against the peripheral lip region of the ceiling panel around the mounting opening. Once this occurs, the lighting device tends to be displaced in position, skewed, damaged and/or separated from the ceiling. This problem has been reported when the disastrous Kobe Earthquake occurred recently.